Fixed cellular is a new facet of cellular technology. In general, fixed cellular is a means by which a plurality of plain ordinary telephone service connections are connected with cellular terminals. The cellular terminals are then capable of conducting radio communication with a cellular network. The multiline fixed cellular network is usually connected to a public switched telephone network. Fixed cellular is mainly being used in developing countries where the cost of running land lines is prohibitive. In these markets, fixed cellular provides a less expensive method of providing phone service to both residential and business customers. In addition, a multiline fixed cellular system may be utilized in many different special-use applications.
Multiline is one facet of fixed cellular technology. In a multiline system, a number of cellular terminals are connected to a generally large number of plain ordinary telephone service connections. The cellular terminals spend their time in one of two modes. In the first mode, a cellular terminal is on a call and acts much like a normal mobile station, that is, all transactions that occur are meant for the mobile on the call. Therefore, when a plain ordinary telephone service connection is validly paged by a radio signal from the cellular network, the plain ordinary telephone service connection utilizes a cellular terminal to conduct communication.
In the second mode of operation, a cellular terminal constantly monitors incoming pages on a dedicated control channel. Since there are more plain ordinary telephone service connections than there are cellular terminals, each cellular terminal in a multiline fixed cellular terminal unit must be able to respond to many different identification numbers. The identification numbers are used to identify each plain ordinary telephone service connection connected to the system. During operation, the dedicated control channel receives a plurality of frames that could contain a page for the cellular terminal. Each frame may contain up to five incoming pages and the rules of PCH displacement dictate that a cellular terminal may have to check up to eight frames in order to locate incoming pages. That means that for each plain ordinary telephone service connection that the cellular terminal is monitoring pages for the cellular terminal may have to perform 40 identification number comparisons every superframe. Preferred multiline fixed cellular network systems are expected to support up to at least 288 plain ordinary telephone service connections. This would require a total of 11,520 (five incoming pages.times.eight frames.times.288 plain ordinary telephone service connections) comparisons to occur in a hyperframe.
Currently, cellular terminals do not have the processing power to perform this high number of comparisons in the time required. The incoming pages come in at such a fast rate that the cellular terminals' processor cannot handle that many comparisons in that short a time frame. To make matters worse, the pages for different plain ordinary telephone service connections occur in different frames within the superframe. As a result, the cellular terminal would have to use more processing power to determine which frames to check against the plain ordinary telephone service connection identification numbers. This could require as much processing power as checking each of the plain ordinary telephone service connection identification numbers themselves.
There are several proposed methods to attempt to reduce the processing power required by the cellular terminals to perform the large number of identification number comparisons. The first method to reduce the processing power required by cellular terminals is to place all of the pages for a given cellular terminal in one frame. Although this would not reduce the number of identification number comparisons, it would greatly reduce the amount of processing power required to keep track of which identification number gets paged in which frame. The problem with this method is that it would require costly and time-consuming changes to existing base station technology.
Another method to reduce the processing power required by the cellular terminals would be to use subaddressing. Subaddressing is a method used by the mobile switching center in which the mobile switching center would send a page to the cellular terminal with a single identification number. If the identification number matches one that is assigned to the cellular terminal, the cellular terminal will check further addressing information to determine which plain ordinary telephone service connection the page is identifying. This would greatly reduce the number of identification number comparisons that the cellular terminals would have to perform, but current mobile switching centers do not support subaddressing, and are not expected to within the time frame which multiline fixed cellular systems will be introduced.
Another method to reduce the processing power required by the cellular terminals would be to perform a binary search through the identification numbers. If the cellular terminal were responsible for 288 identification numbers, this would require only ten identification number comparisons for each identification number contained within the frame. There may be up to 28 frames per superframe that may contain pages for the cellular terminal. This would greatly reduce the number of identification number comparisons required by the cellular terminal. The number of identification number comparisons for this method is 1,400 (five pages.times.ten comparisons.times.28 frames) per superframe. While the binary search algorithm is one of the better methods to reduce the processing power required, it would still require 1,400 comparisons per superframe. This presents a significant problem because it is expected that 1,400 identification number comparisons per superframe would still be outside of the realm of what the processing power of the cellular terminals could accomplish. In addition, increasing the number of identification numbers which the cellular terminal supports will increase the number of comparisons.
As such, a need exists for a multiline fixed cellular system that can support a plurality of plain ordinary telephone service connections and has the processing power to handle the fast incoming page rate.